Wireless networks allow computing devices to share information and resources via wireless communications. Examples of computing devices used in wireless networks include laptop or desktop computers, personal digital assistants (PDAs), mobile phones such as cellular radiotelephones and satellite radiotelephones, data terminals, data collection devices, personal digital assistants (PDAs) and other portable and non-portable computing devices. One broad family of standards developed to facilitate wireless networking is set forth in the IEEE 802.11 standard. The original IEEE 802.11 standard provides data transfer rates of 1–2 Megabits per second (Mbps) in a 2.4–2.483 Gigahertz (GHz) frequency band (hereafter the 2.4 GHz band). However, a number of extensions to the original IEEE 802.11 standard have been developed in an effort to increase data transfer rates.
The IEEE 802.11b standard (sometimes referred to as 802.11 wireless fidelity or 802.11 Wi-Fi) is an extension of the IEEE 802.11 standard that provides 11 Mbps transmission (with a fallback to 5.5, 2.0 and 1.0 Mbps) in the 2.4 GHz band. The IEEE 802.11b standard utilizes binary phase shift keying (BPSK) for 1.0 MBPS transmission, and quadrature phase shift keying (QPSK) for 2.0, 5.5 and 11.0 Mbps transmission. Complimentary code keying (CCK) techniques are also employed by the IEEE 802.11b standard in order to achieve multi-channel operation in the 2.4 GHz band for the 5.0 and 11.0 Mbps transmission rates.
The IEEE 802.11g standard is another extension of the IEEE 802.11 standard. The IEEE 802.11g standard utilizes orthogonal frequency division multiplexing (OFDM) in the 2.4 GHz frequency band to provide data transmission at rates up to 54 Mbps. The IEEE 802.11g standard also provided backwards capability with 802.11b networks. The IEEE 802.11a standard is an extension of IEEE 802.11 standard that utilizes OFDM in a 5 GHz frequency band to provide data transmission at rates up to 54 Mbps. These and other wireless networks have been developed. Additional extensions to the IEEE 802.11 standard, as well as other WLAN standards will likely emerge in the future.
Wireless networks may contain one or more access points that interface with wireless and/or wired networks. Access points may also interface wirelessly with other access points to extend the geographical size of the wireless network. In addition, wireless routers may be used in wireless networks to perform data routing functions within the wireless setting and possibly extend the size of the wireless network. Sometimes, both wireless routers and access points are used together to form a relatively large wireless network environment.
Wireless communication devices that support wireless networking standards may also support other communication standards, such as standards commonly used for voice communications. The voice communication standards may be based on one or more of a variety of modulation techniques, such as frequency division multiple access (FDMA), time division multiple access (TDMA), and various spread spectrum techniques. One common spread spectrum technique used in wireless voice communication is code division multiple access (CDMA) signal modulation. In CDMA, multiple communications are simultaneously transmitted over a spread spectrum radio frequency (RF) signal. Other wireless communication systems may use different modulation techniques. For example, GSM systems use a combination of TDMA and FDMA modulation techniques. These techniques are also used in other systems related to GSM systems, including the DCS1800 and PCS1900 systems, which operate at 1.8 GHz and 1.9 GHz, respectively.
Frequency synthesizers are commonly implemented within wireless communication devices to facilitate RF signal reception and RF signal transmission. For example, during RF signal reception, RF signals are typically mixed down to baseband signals, which can be converted to digital values and demodulated. Reference waveforms are produced by a frequency synthesizer and mixed with an RF waveform to generate the baseband signals. The process of mixing an RF waveform down to baseband is sometimes referred to as a down-conversion process.
Frequency synthesizers are also used during RF signal transmission. In that case, baseband signals are up-mixed to RF (sometimes referred to as an up-conversion process). During the up-conversion process, the frequency synthesizer produces reference waveforms which are modulated with the baseband signal before being wirelessly transmitted. For example, the reference waveform may be created by a voltage controlled oscillator (VCO) having a frequency that is determined by a phase locked loop (PLL). The timing reference for the PLL may be high precision low frequency crystal oscillator, such as a voltage controlled temperature compensated crystal oscillator (VCTCXO).
RF waveforms associated with voice communication standards typically have a different frequency than RF waveforms associated with wireless networking standards such as IEEE 802.11 standards. For example, as mentioned above, many IEEE 802.11 standards operate in the 2.4 GHz band. Voice communication standards, on the other hand typically operate in frequency bands different than the 2.4 GHz band, such as a 800 MHz band, a 1800 MHz band, or a 1900 MHz band. For this reason, conventional wireless communication devices that support both voice communication standards and wireless networking standards typically utilize different frequency synthesizers to generate waveforms at the frequencies required by the different standards.